/**
 * Copyright (DigitalChina) 2016-2020, DigitalChina.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.dc.city.common.utils;

import java.io.ByteArrayOutputStream;

/**
 * 使用base64算法对前台穿过来的字符串进行解密
 *
 * @author xutaog
 * @version V1.0 创建时间：2015年8月3日 下午4:42:10
 *          Copyright 2015 by DigitalChina
 */
public class Base64EncodeUtils {

    private static byte[] base64DecodeChars = new byte[] { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4,
            5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26,
            27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1,
            -1, -1, -1 };

    /**
     * 解密
     * 
     * @param str
     * @return
     */
    public static byte[] decode(String str) {
        byte[] returnData = null;
        try{
            byte[] data = str.getBytes();
            int len = data.length;
            ByteArrayOutputStream buf = new ByteArrayOutputStream(len);
            int i = 0;
            int b1, b2, b3, b4;

            while (i < len) {
                do {
                    b1 = base64DecodeChars[data[i++]];
                } while (i < len && b1 == -1);
                if (b1 == -1) {
                    break;
                }

                do {
                    b2 = base64DecodeChars[data[i++]];
                } while (i < len && b2 == -1);
                if (b2 == -1) {
                    break;
                }
                buf.write((int) ((b1 << 2) | ((b2 & 0x30) >>> 4)));

                do {
                    b3 = data[i++];
                    if (b3 == 61) {
                        return buf.toByteArray();
                    }
                    b3 = base64DecodeChars[b3];
                } while (i < len && b3 == -1);
                if (b3 == -1) {
                    break;
                }
                buf.write((int) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));

                do {
                    b4 = data[i++];
                    if (b4 == 61) {
                        return buf.toByteArray();
                    }
                    b4 = base64DecodeChars[b4];
                } while (i < len && b4 == -1);
                if (b4 == -1) {
                    break;
                }
                buf.write((int) (((b3 & 0x03) << 6) | b4));
                returnData = buf.toByteArray();
            }
        }catch(Exception e){
            e.printStackTrace();
        }
        return returnData;
    }
}
